Mutations in TOP1 and TACSTD2, which encode topoisomerase-1 and TROP-2 respectively, were found to be associated with acquired resistance in SG.26 CDK12 is a member of the cyclin-dependent kinase (CDK) family, and genomic alterations in CDK12 have been reported in breast cancer. The gene discussed is TACSTD2; the disease is breast carcinoma.